Position Estimating System, Radio Communication Apparatus, Program, Position Estimating Method and Information Server

ABSTRACT

A radio communication apparatus has a storage section for correlating and storing positional information and identification information of the base station, a receiving section for receiving radio signals transmitted from the base station and containing the identification information and a position estimating section for estimating position of the radio communication apparatus based on the positional information stored in the storage section. In the storage section, the positional information of a first base station within a first coverage is represented by using a first discrete value obtained by quantizing the position of the first base station by setting the first coverage as a quantization coverage and a first quantization number as a quantization number and the positional information of a second base station within a second coverage whose area is narrower than the first coverage and where the base stations are more densely installed than the first coverage is represented by using a second discrete value obtained by quantizing the position of the second base station by setting the second coverage as a quantization coverage and a second quantization number that is smaller than the first quantization number as a quantization number.

TECHNICAL FIELD

The present invention relates to a radio communication system, a radiocommunication apparatus, a program, a position estimating method and aninformation server.

BACKGROUND ART

Lately, a receiver capable of receiving radio signals transmitted fromsatellites has come to be mounted in mobiles such as cars and portablephones. It has then become possible to estimate position of the mobilecarrying such receiver by positioning by means of GPS (GlobalPositioning System). The technology for estimating position by usingsuch receiver is a common basic technology essential in a variety offields such as navigation, security, entertainment and others. However,the position estimating technology based on positioning by means of theGPS has had problems that it takes a long time for synchronizationacquisition in starting the positioning and that it is difficult to beused within a house or basement where the radio signals from thesatellites do not reach.

The Patent Document 1 has disclosed a technology that enables PHS(Personal Handyphone System) to measure strength of signals transmittedfrom base stations to estimate its own position based on the strength ofthe measured signals. Specifically, communication providers place thebase stations of the PHS, so that positions where they have beeninstalled are normally known. Therefore, the PHS can estimate its ownposition by the principle of triangulation based on the positions of therespective base stations by measuring the strength of the signalstransmitted from three or more base stations and by estimating distancesbetween the respective base stations and its own position based on thestrength of the measured signals.

It is also conceivable to provide a position estimating method thatenables a radio communication apparatus that communicates wirelesslywith base stations (access points) of a wireless LAN (Local AreaNetwork) to measure strength of signals transmitted from the basestations to estimate the position of the radio communication apparatusbased on the signal strength. For instance, the base station of thewireless LAN transmits beacons for announcing its existence to itssurroundings at certain frequency (e.g., 5 times/sec.). The radiocommunication apparatus can estimate its own position based on thesignal strength of the beacon and position of the base station of thewireless LAN stored in advance. This position estimating method enablesthe estimation of position even within a house or basement that has beendifficult by the position estimating technology based on positioning byGPS because the base station of the wireless LAN may be installed withinthe house and basement. That is, the position estimating methoddescribed above may be a very convenient and simple position estimatingtechnology, provided that the radio communication apparatus is arrangedto store base station information indicating positions of the basestations of the wireless LAN installed around the radio communicationapparatus.

PRIOR ART DOCUMENT

[Patent Document 1] Japanese Unexamined Patent Application PublicationNo. 2006-171012

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, the conventional position estimating method has had a problemthat a memory capacity required for the radio communication apparatusincreases because in accordance with the increase of the number of basestations of wireless LAN, the data amount of the base stationinformation increases.

Accordingly, the present invention has been made in view of the aboveproblems, and the present invention aims to provide a novel and improvedposition estimating system, radio communication apparatus, program,position estimating method, and information server, capable ofsuppressing the memory capacity required for the radio communicationapparatus.

Means for Solving the Problems

In order to solve the above problems, according to an aspect of thepresent invention, there is provided a position estimating systemincluding a radio communication apparatus capable of wirelesslycommunicating with one or more base stations, and an information servercapable of communicating with the radio communication apparatus. Theinformation server includes a quantizing section for representingpositional information of a first base station located in a firstcoverage by using a first discrete value obtained by quantizing theposition of the first base station by setting the first coverage as aquantization coverage and a first quantization number as a quantizationnumber and for representing positional information of a second basestation located in a second coverage whose area is narrower than thefirst coverage and where the base stations are more densely installedthan the first coverage by using a second discrete value obtained byquantizing the position of the second base station by setting the secondcoverage as a quantization coverage and a second quantization numberthat is smaller than the first quantization number as a quantizationnumber, and a first storage section for storing base station informationin which the positional information represented by using the firstdiscrete value or the second discrete value by the quantizing section iscorrelated with identification information of the base station. Theradio communication apparatus includes an obtaining section forobtaining the base station information that is transmitted from thetransmitted section and stored in the first storage section, a secondstorage section for storing the base station information obtained by theobtaining section, a receiving section for receiving radio signalscontaining the identification information of the base stationtransmitted from the base station, and a position estimating section forextracting the positional information of the base station indicated bythe identification information contained in the radio signals from thepositional information stored in the storage section and estimating theposition of the radio communication apparatus based on the extractedpositional information.

Furthermore, in order to solve the above problems, according to anotheraspect of the present invention, there is provided a radio communicationapparatus capable of wirelessly communicating with one or more basestations, including a storage section for correlating and storingpositional information and identification information of the basestation, a receiving section for receiving radio signals transmittedfrom the base station and containing the identification information ofthe base station, and a position estimating section for extracting thepositional information of the base station indicated by theidentification information contained in the radio signals from thepositional information stored in the storage section and estimating theposition of the radio communication apparatus based on the extractedpositional information. In the storage section, the positionalinformation of a first base station located in a first coverage isrepresented by using a first discrete value obtained by quantizing theposition of the first base station by setting the first coverage as aquantization coverage and a first quantization number as a quantizationnumber and the positional information of a second base station locatedin a second coverage whose area is narrower than the first coverage andwhere the base stations are more densely installed than the firstcoverage is represented by using a second discrete value obtained byquantizing the position of the second base station by setting the secondcoverage as a quantization coverage and a second quantization numberthat is smaller than the first quantization number as a quantizationnumber.

Such configuration allows an information amount required forrepresenting the second discrete value to be suppressed more than aninformation amount required for representing the first discrete valuebecause the second quantization number is smaller than the firstquantization number. Here, the density of the base stations located inthe second coverage is higher than that of the base stations located inthe first coverage. Therefore, the radio communication apparatus mayhold the positional information of the base stations located in thefirst coverage and the second coverage while suppressing the informationamount as compared to a case of simply quantizing the first coverage andthe second coverage altogether.

Moreover, the first quantization number or the second quantizationnumber may be a value that keeps a quantization error of the firstdiscrete value or the second discrete value within a range of 0.5 m to 4m. Here, there may be a case where the accurate position of the basestation is unclear even if precision of the first discrete value or thesecond discrete value representing the positional information of thebase station is high and does not contribute for more accurate positionestimation of the radio communication apparatus. Then, the informationamount for representing the first discrete value or the second discretevalue may be suppressed while keeping the precision of the estimation ofposition of the radio communication apparatus by setting the precisionof the first discrete value or the second discrete value within therange of 0.5 m to 4 m.

The first coverage may be a coverage excluding the second coverage froma predetermined coverage overlapping with the second coverage. In suchconfiguration, the second coverage does not overlap with the firstcoverage. Accordingly, it is possible to prevent plural positionalinformation of the same base station from being stored in the storagesection.

Moreover, a plurality of second coverages may be contained in thepredetermined coverage. For instance, because the density of basestations is considered to be relatively high in urban areas, secondcoverages such as Tokyo, Osaka, New York and the like may be containedin a predetermined coverage when the whole world is set to be thepredetermined coverage.

Moreover, the quantization error of the second discrete value may belarger than the quantization error of the first discrete value. Here,the radio communication apparatus may estimate position at higherprecision when it receives radio signals from more base stations.Moreover, the density of base stations located in the second coverage ishigher than that of base stations located in the first coverage withrespect to this radio communication apparatus. Therefore, there may be acase where the quantization error of the second discrete value may belarger than the quantization error of the first discrete value asdescribed above in order to realize the position estimation in thesecond coverage and the position estimation in the first coverage madeby the radio communication apparatus at the same degree of precision. Asa result, the information amount for representing the second discretevalue may be suppressed while keeping the precision of positionestimation by the radio communication apparatus.

Moreover, in order to solve the above problems, according to anotheraspect of the present invention, there is provided a program foroperating a computer as a radio communication apparatus capable ofwirelessly communicating with one or more base stations and includes areceiving section for receiving radio signals transmitted from the basestation and containing identification information of the base stationand a position estimating section for extracting the positionalinformation of the base station indicated by the identificationinformation contained in the radio signals from a storage mediumcorrelating and storing the positional information and theidentification information of the base station to estimate the positionof the radio communication apparatus based on the extracted positionalinformation. In the storage medium, the positional information of afirst base station located in a first coverage is represented by using afirst discrete value obtained by quantizing the position of the firstbase station by setting the first coverage as a quantization coverageand a first quantization number as a quantization number, and thepositional information of a second base station located in a secondcoverage whose area is narrower than the first coverage and where thebase stations are more densely installed than the first coverage isrepresented by using a second discrete value obtained by quantizing theposition of the second base station by setting the second coverage as aquantization coverage and a second quantization number that is smallerthan the first quantization number as a quantization number.

Such program can allow hardware resources of the computer including, forexample, a CPU, a ROM or a RAM to execute the functions of the receivingsection and the position estimating section as described above. That is,the computer using the program may function as the radio communicationapparatus described above.

Moreover, in order to solve the above problems, according to anotherembodiment of the present invention, there is provided a positionestimating method executed in a radio communication apparatus capable ofwirelessly communicating with one or more base stations and includes thesteps of receiving radio signals transmitted from the base station andcontaining identification information of the base station and extractingthe positional information of the base station indicated by theidentification information contained in the radio signals from a storagemedium correlating and storing the positional information of the basestation and the identification information, and estimating the positionof the radio communication apparatus based on the extracted positionalinformation. In the storage medium, the positional information of afirst base station located in a first coverage is represented by using afirst discrete value obtained by quantizing the position of the firstbase station by setting the first coverage as a quantization coverageand a first quantization number as a quantization number, and thepositional information of a second base station located in a secondcoverage whose area is narrower than the first coverage and where thebase stations are more densely installed than the first coverage isrepresented by using a second discrete value obtained by quantizing theposition of the second base station by setting the second coverage as aquantization coverage and a second quantization number that is smallerthan the first quantization number as a quantization number.

Moreover, in order to solve the above problems, according to anotherembodiment of the present invention, there is provided an informationserver capable of communicating with a radio communication apparatuscapable of wirelessly communicating with one or more base stations. Theinformation server includes a quantizing section for representingpositional information of a first base station located in a firstcoverage by using a first discrete value obtained by quantizing theposition of the first base station by setting the first coverage as aquantization coverage and a first quantization number as a quantizationnumber, and for representing positional information of a second basestation located in a second coverage whose area is narrower than thefirst coverage and where the base stations are more densely installedthan the first coverage by using a second discrete value obtained byquantizing the position of the second base station by setting the secondcoverage as a quantization coverage and a second quantization numberthat is smaller than the first quantization number as a quantizationnumber, a storage section for storing base station information in whichthe positional information represented by using the first discrete valueor the second discrete value by the quantization section are correlated;and a communication section for transmitting the base stationinformation stored in the storage section to the radio communicationapparatus.

Such configuration allows the information amount required forrepresenting the second discrete value to be suppressed more than theinformation amount required for representing the first discrete valuebecause the second quantization number is smaller than the firstquantization number. Here, the density of the base stations located inthe second coverage is higher than that of the base stations located inthe first coverage. Therefore, the information server may transmit thebase station information of the base stations located in the firstcoverage and the second coverage whose information amount is suppressedto the radio communication apparatus as compared to the case of simplyquantizing the first coverage and the second coverage altogether. As aresult, it becomes possible to reduce an amount of communication withthe radio communication apparatus and a memory capacity required for theradio communication apparatus.

EFFECT OF THE INVENTION

As described above, a position estimating system, a radio communicationapparatus, a program, a position estimating method, and an informationserver according to the present invention can suppress the memorycapacity required for the radio communication apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram showing a configuration example of aradio communication system according to the present embodiment;

FIG. 2 is a block diagram showing a hardware configuration of a radiocommunication apparatus according to the embodiment;

FIG. 3 is a functional block diagram showing configurations of the radiocommunication apparatus and an information server included in a positionestimating system according to the embodiment;

FIG. 4 is an explanatory diagram showing one example of signal strengthsmeasured by a measuring section;

FIG. 5 is an explanatory diagram showing a reference example of a formof base station information;

FIG. 6 is an explanatory diagram showing a concrete example ofquantization performed by a quantizing section;

FIG. 7 is an explanatory diagram showing an example of a normal coverageand a base station crowded coverage;

FIG. 8A is an explanatory diagram showing one example of base stationinformation of base stations located in the base station crowdedcoverage recorded in a storage section;

FIG. 8B is an explanatory diagram showing one example of base stationinformation of base stations located in the normal coverage recorded inthe storage section;

FIG. 9 is a sequence diagram showing a flow of a position estimatingmethod executed in the radio communication apparatus and the informationserver; and

FIG. 10 is an explanatory diagram showing an exemplary modification ofthe normal coverage and the base station crowded coverage.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the appended drawings. Inaddition, in this specification and the appended drawings, structuralelements that have substantially the same function and configuration aredenoted with the same reference numerals, and repeated explanation ofthese structural elements is omitted.

“The best mode for carrying out the invention” will be explainedaccording to the following order.

[1] Outline of Radio Communication System according to PresentEmbodiment

[2] Explanation of Position Estimating System according to PresentEmbodiment

-   -   [2-1] Hardware Configuration of Radio Communication Apparatus    -   [2-2] Functional Configuration of Radio Communication Apparatus        and Information Server    -   [2-3] Operations of Radio Communication Apparatus and        Information Server

[3] Conclusion

[1] OUTLINE OF RADIO COMMUNICATION SYSTEM ACCORDING TO PRESENTEMBODIMENT

First, an outline of a radio communication system 1 according to thepresent embodiment will be explained with reference to FIG. 1.

FIG. 1 is an explanatory diagram showing a configuration example of aradio communication system 1 according to the present embodiment. Asshown in FIG. 1, the radio communication system 1 includes a radiocommunication apparatus 20 and a plurality of base stations 30A through30D. In addition, the base stations 30A through 30D will be referredsimply as the base stations 30 unless specifically required todistinguish the base stations 30A through 30D.

The base stations 30 are base stations (access points) of a wireless LAN(Local Area Network) of IEEE 802.11 series (e.g., 802.11b, 802.11g andthe like) based on WiFi (Wireless Fidelity) Standard, for example.

Such base station 30 can periodically transmit beacon signals forannouncing its existence to its surroundings besides signals transmittedin relaying radio communications. The beacon signal contains a basestation ID as identification information uniquely given to the basestation 30, for example.

The radio communication apparatus 20 correlates and stores positionalinformation indicating positions of respective base stations 30 and thebase station IDs of the base stations 30 as the base stationinformation. Accordingly, on receiving the beacon signals from thesurrounding base stations 30, the radio communication apparatus 20 mayextract the positional information of the base station indicated by thebase station ID contained in the beacon signal from the stored basestation information and may estimate its own position based on theextracted positional information.

A concrete example of the position estimating method by means of theradio communication apparatus 20 will be described later with referenceto FIG. 4. Forms of the base station information stored in the radiocommunication apparatus 20 will be also described later with referenceto FIGS. 6 through 8.

In addition, although FIG. 1 shows a note-type PC as one example of theradio communication apparatus 20, the radio communication apparatus 20may be an information processor or a portable device such as a PC(Personal Computer), a domestic image processor (such as DVD recorderand video deck), a portable telephone, a PHS (Personal HandyphoneSystem), a portable music player, a portable video player, a PDA(Personal Digital Assistant), a domestic game machine, a portable gamemachine and appliances.

[2] EXPLANATION OF POSITION ESTIMATING SYSTEM ACCORDING TO PRESENTEMBODIMENT

Next, a position estimating system according to the present embodimentwill be explained. The position estimating system includes the radiocommunication apparatus 20 and an information server 10 that transmitsbase station information to the radio communication apparatus 20.

In the explanation of the position estimating system, functionalconfigurations and operations of the radio communication apparatus andthe information server will be explained after explaining a hardwareconfiguration of the radio communication apparatus 20.

[2-1] Hardware Configuration of Radio Communication Apparatus

FIG. 2 is a block diagram showing a hardware configuration of the radiocommunication apparatus 20 according to the present embodiment. Theradio communication apparatus 20 includes a CPU (Central ProcessingUnit) 201, a ROM (Read Only Memory) 202, a RAM (Random Access Memory)203, a host bus 204, a bridge 205, an external bus 206, an interface207, an input device 208, an output device 210, a storage device (HDD)211, a drive 212 and a communication device 215.

The CPU 201 functions as an arithmetic processing unit and a controllingunit and controls overall operations within the radio communicationapparatus 20 in accordance with various programs. The CPU 201 may be amicroprocessor as well. The ROM 202 stores programs, computationparameters and the like used by the CPU 201. The RAM 203 primarilystores programs used when the CPU 201 executes, parameters thatoccasionally change in the execution thereof, and the like. These aremutually connected by the host bus 204 formed by a CPU bus and others.

The host bus 204 is connected to the external bus 206 such as a PCI(Peripheral Component Interconnect/Interface) bus via the bridge 205. Inaddition, it is not always necessary to separately construct the hostbus 204, the bridge 205 and the external bus 206 and their functions maybe mounted in one bus.

The input device 208 is composed of input means for enabling a user toinput information such as a mouse, a keyboard, a touch panel, buttons, amicrophone, a switch and a lever and an input control circuit forgenerating input signals based on the input by the user and foroutputting them to the CPU 201. The user of the radio communicationapparatus 20 may input various data and instruct processing operationsto the radio communication apparatus 20 by manipulating the input device208.

The output device 210 is composed of a display unit such as a CRT(Cathode Ray Tube) display and a LCD (liquid crystal display) and alamp, and a sound output device such as a speaker and a headphone. Theoutput device 210 outputs reproduced contents, for example.Specifically, the display unit displays various information such asreproduced image data by texts or images. Meanwhile, the sound outputdevice converts reproduced sound data and others into sounds to output.

The storage device 211 is a device for storing data configured as oneexample of a storage section of the radio communication apparatus 20according to the present embodiment and may include a storage medium, arecording device for recording data in the storage medium, a readingdevice for reading data out of the storage medium, a deleting device fordeleting data recorded in the storage medium, and others. The storagedevice 211 may be composed of a HDD (Hard Disk Drive), for example. Thestorage device 211 drives a hard disk and stores programs to be executedby the CPU 201 and various data. Base station information describedlater is also recorded in the storage device 211.

The drive 212 is a reader-writer for the storage medium and is built inor is externally attached to the radio communication apparatus 20. Thedrive 212 reads out information recorded in a removable storage medium24 such as a magnetic disk, an optical disk, an optic-magnetic disk anda semiconductor memory that is mounted thereon and outputs theinformation to the RAM 203.

The communication device 215 is a communication interface composed of acommunication device and others for being connected to a communicationnetwork 12, for example. Moreover, the communication device 215 may be acommunication unit compatible with wireless LAN (Local Area Network) orwith wireless USB or a wired communication unit that communicatesthrough wires. The communication network 12 may include wire cables suchas copper lines and optical fibers, transmission paths of data such asradio waves, and data relay device such as routers and base stations 30for controlling communications. That is, the communication device 215transmits and receives the beacon signals and various data with the basestations 30. In addition, the various data may be arbitrary data such asmusic data such as music, lectures and radio programs, image data suchas movies, TV programs, video programs, pictures, documents, drawingsand charts as well as games and software.

In addition, a hardware configuration of the information server 10 maybe arranged substantially in the same manner as the hardwareconfiguration of the radio communication apparatus 20, so that itsexplanation is omitted.

[2-2] Functional Configuration of Radio Communication Apparatus andInformation Server

FIG. 3 is a functional block diagram showing configurations of the radiocommunication apparatus 20 and the information server 10 included in theposition estimating system according to the present embodiment. As shownin FIG. 3, the information server 10 includes a communication section104, a base station information input section 108, a quantizing section112 and a storage section 116. The radio communication apparatus 20includes a communication section 216, a measuring section 220, aposition estimating section 224, an application section 228, a storagesection 232 and a base station information obtaining section 236.

The communication section 216 is an interface between the radiocommunication apparatus 20 and the base station 30 and has functions asreceiving and transmitting sections. For instance, the communicationsection 216 may receive signals transmitted from the base station 30.The communication section 216 also has a function as an interfacebetween the radio communication apparatus 20 and the information server10. For instance, the communication section 216 may transmit a requestfor obtaining base station information to the information server 10 andmay receive the base station information from the information server 10.

The measuring section 220 measures receiving strengths of the signalstransmitted from the respective base stations 30 and received by thecommunication section 216. FIG. 4 shows one example of signal strengthsmeasured by the measuring section 220 when the radio communicationapparatus 20 has a positional relationship with the respective basestations 30 as shown in FIG. 1.

FIG. 4 is an explanatory diagram showing one example of signal strengthsmeasured by the measuring section 220. In FIG. 4, reference numerals andcharacters denoting the respective base stations 30 are supposed toindicate the base station IDs of the respective base stations 30 forconvenience of explanation. Specifically, FIG. 4 shows a case where thereceiving strength of the signals transmitted from the base station 30Awhose base station ID is “30A” is “−90 Dbm”, the receiving strength ofthe signals transmitted from the base station 30B whose base station IDis “30B” is “−70 Dbm”, the receiving strength of the signals transmittedfrom the base station 30C whose base station ID is “30C” is “−80 Dbm”and the receiving strength of the signals transmitted from the basestation 30D whose base station ID is “30D” is “−75 Dbm”.

Meanwhile, the storage section 232 (second storage section) correlatesand stores base station IDs of the base stations 30 wirelesslycommunicating with the radio communication apparatus 20 and positionalinformation indicating the installation sites of the respective basestations 30 as the base station information. A concrete example of thebase station information stored in the storage section 232 will bedescribed later with reference to FIG. 8. In addition, the storagesection 232 may be a storage medium such as a non-volatile memory suchas an EEPROM (Electrically Erasable Programmable Read-Only Memory) andan EPROM (Erasable Programmable Read Only Memory), a magnetic disk suchas a hard disk and a disk type magnetic medium, an optical disk such asa CD-R (Compact Disk Recordable)/RW (ReWritable), a DVD-R (DigitalVersatile Disk Recordable)/RW/+R/+RW/RAM (Random Access Memory) and a BD(Blu-Ray Disc (trade mark))-R/BD-RE, and a MO (Magneto Optical) disk.

The position estimating section 224 estimates the position of the radiocommunication apparatus 20 based on the signal strength measured by themeasuring section 220 and the base station information stored in thestorage section 232. For instance, the position estimating section 224estimates the position of the radio communication apparatus 20 based onthe following Equation 1:

$\begin{matrix}{O = {\frac{1}{W} \cdot {\sum\limits_{i}\; \left( {{Wi} \cdot {Ai}} \right)}}} & {{Eq}.\mspace{14mu} 1} \\{{Wi} = \frac{1}{{distS}\left( {O,{Ai}} \right)}} & {{Eq}.\mspace{14mu} 2} \\{W = {\sum\limits_{i}\; {Wi}}} & {{Eq}.\mspace{14mu} 3}\end{matrix}$

In Equation 1, Ai indicates positional information of i-th base station30 registered in the storage section 232. Accordingly, when thepositional information of the base station 30 is expressed by longitudeand latitude, Equation 1 is applied to longitude and latitude,respectively. Wi is a weighting factor obtained based on distS (O, Ai)indicating a distance between the radio communication apparatus 20 andthe i-th base station 30 estimated from the signal strength as expressedby Equation 2. W is a total sum of the weighting factors as expressed byEquation 3.

When reference is made to Equation 1, positional information of the basestation 30 whose distS (O, Ai) is small is largely reflected to theestimated position O of the radio communication apparatus 20 at eachmeasuring time. Meanwhile, positional information of the base station 30whose distS (O, Ai) is large is less influential to the estimatedposition O of the radio communication apparatus 20.

The position estimating section 224 can rationally estimate thepositional information of the radio communication apparatus 20 by usingsuch Equation 1. That is, the position estimating section 224 canextract the positional information (Ai) with which the base station IDof the base station 30 contained in the signals received by thecommunication section 216 is correlated in the storage section 232, andcan estimate the position of the radio communication apparatus 20 basedon the extracted positional information and the signal strength measuredby the measuring section 220. The position estimating section 224 canalso obtain an address such as “5th St., C Ward, AB Prefecture” based onthe estimated positional information.

In addition, in the present embodiment, since quantized positionalinformation is stored in the storage section 232, the positionestimating section 224 also has a function as a decoding section forconverting the quantized positional information into longitude andlatitude.

In addition, the position estimating method of the radio communicationapparatus 20 is not limited to the method of using Equation 1 describedabove, and for instance, position of the base station 30 that is thesource of signals whose receiving strength is the highest in the radiocommunication apparatus 20 may be estimated as the position of the radiocommunication apparatus 20. Moreover, a center position of the basestations 30 that is the source of signals whose receiving strengthexceeds a threshold value in the radio communication apparatus 20 may beestimated as the position of the radio communication apparatus 20.

Furthermore, a center position of the base station 30 that is the sourceof signals whose receiving strength in the radio communication apparatus20 falls within a predetermined rate such as top 10%, 20% and the likemay be estimated as the position of the radio communication apparatus20. Furthermore, a center position of the base stations 30 that is thesource of signals whose receiving strength in the radio communicationapparatus 20 falls within a predetermined order such as top five, tenand the like may be estimated as the position of the radio communicationapparatus 20.

The application section 228 performs processing using the positionestimated by the position estimating section 224. For instance, theapplication section 228 may output (display) the position estimated bythe position estimating section 224 from the output device 210.Moreover, the application section 228 may obtain points corresponding tothe position estimated by the position estimating section 224.Furthermore, the application section 228 may request the user of theradio communication apparatus 20 for authentication processing when theposition estimated by the position estimating section 224 is out of apreset coverage.

The position estimating section 224 can estimate the position of theradio communication apparatus 20 by using the base station informationstored in the storage section 232 as described above. Such base stationinformation is represented in a form shown in FIG. 5, for example.

FIG. 5 is an explanatory diagram showing a reference example of the formof the base station information. As shown in FIG. 5, when the basestation ID is represented by 6 bytes and the longitude and latitude arerepresented by 8 bytes by using double floating points, for example, theamount of information of one base station information is 24 bytes.Accordingly, a storage medium for storing information of one millionbase stations requires a memory capacity of about 24 Mbytes excludinginformation such as an index for efficiently retrieving the information.However, because a memory capacity of the storage section 232 of theradio communication apparatus 20 is limited especially when the radiocommunication apparatus 20 is a portable device, it has been difficultto fully store the base station information each of which is representedby 24 bytes in the storage section 232.

Then, focusing on the circumstances described above, the inventors havecome to create the radio communication apparatus 20 and the informationserver 10 according to the present embodiment. The information server 10according to the present embodiment is capable of representing thepositional information of the base station information while suppressingthe information amount and the radio communication apparatus 20 iscapable of storing the base station information whose information amountis suppressed. A configuration of the information server 10 capable ofsuppressing the information amount of the positional information of thebase station information will be explained below.

The communication section 104 of the information server 10 is aninterface with the radio communication apparatus 20 and has a functionas a transmitting section for transmitting the base station informationstored in the storage section 116 to the radio communication apparatus20. The communication section 104 may also transmit the base stationinformation periodically or in response to a request from the radiocommunication apparatus 20.

The base station information is input to the base station informationinput section 108. The base station information input section 108 mayreceive the base station information manually input or from an externaldevice, for example.

The quantizing section 112 quantizes the positional information of thebase station information input to the base station information inputsection 108 or the positional information of the base stationinformation stored in the storage section 116. The quantizing section112 also has a function as a recording section for recording thequantized base station information in the storage section 116.

The quantizing section 112 according to the present embodiment canquantize, within a predetermined coverage, base station information ofbase stations located in a normal coverage (first coverage) and a basestation crowded coverage (second coverage) where density of the basestations 30 is higher than that of the normal coverage and whose area issmaller than that of the normal coverage, by different conditions(quantization coverages and quantization numbers). FIG. 7 shows aconcrete example of the normal coverage and the base station crowdedcoverage.

FIG. 7 is an explanatory diagram showing the example of the normalcoverage and the base station crowded coverage. In the example shown inFIG. 7, the base station crowded coverage 42 is the Kanto area where thebase stations 30 are crowded and the normal coverage 40 is a coverageexcluding the base station crowded coverage 42 within the predeterminedcoverage including Japan. In addition, selection of the base stationcrowded coverage 42 and the normal coverage 40 may be made manually orautomatically based on the distribution of the base stations.

The quantizing section 112 represents the positional information of thebase station located in the normal coverage 40 by using bit values(first discrete value) obtained by quantizing the position of the basestation by setting the normal coverage 40 as a quantization coverage anda first quantization number as a quantization number. Meanwhile, thequantizing section 112 represents the positional information of the basestation located in the base station crowded coverage 42 by using bitvalues (second discrete value) obtained by quantizing the position ofthe base station by setting the base station crowded coverage 42 as aquantization coverage and a second quantization number that is smallerthan the first quantization number as a quantization number.

Here, the quantization includes meaning of representing continuousamount (e.g., positional information such as longitude and latitude) bydiscontinuous bit values. The quantization number is a value indicatingthat the continuous amount within the quantization coverage should berepresented by how many bits (how many steps of discrete values).Accordingly, the smaller the quantization number, the more theinformation amount (bit numbers) for representing the positionalinformation is suppressed.

Because the quantizing section 112 described above represents thepositional information of the base station located in the base stationcrowded coverage 42 by using the bit values obtained by quantizing theposition of the base station by setting the base station crowdedcoverage 42 as the quantization coverage and the second quantizationnumber that is smaller than the first quantization number as thequantization number, it is possible to suppress the information amountfor representing the positional information of the base stations withinthe base station crowded coverage 42. A concrete example of quantizationperformed by the quantizing section 112 will be explained with referenceto FIG. 6.

FIG. 6 is an explanatory diagram showing the concrete example ofquantization performed by the quantizing section 112. As shown in FIG.6, the base station crowded coverage 42 is a rectangular area havinglongitudinal distance w and latitudinal distance h, starting from (sx,sy). Here, a number for longitudinally dividing the base station crowdedcoverage 42, i.e., a longitudinal quantization number of the basestation crowded coverage 42, is denoted by α, and a number forlatitudinally dividing the base station crowded coverage 42, i.e., alatitudinal quantization number, by β. When the longitudinalquantization number of the base station crowded coverage 42 is denotedby α and the latitudinal quantization number as β as described above,the second quantization number is a value obtained by multiplying α andβ.

When the bit number obtained by longitudinally quantizing the basestation crowded coverage 42 is denoted by a bit value a and the bitnumber obtained by latitudinally quantizing the base station crowdedcoverage 42 is denoted by a bit value b, the longitude x and latitude ycontained in the base station crowded coverage 42 may be expressed bythe following Equations 4 and 5:

x=sx+(w/α)·a  Eq. 4

y=sy+(h/β)·b  Eq. 5

The quantizing section 112 can calculate the bit values a and b from thepositional information x and y as shown in Equations 4 and 5. That is,the quantizing section 112 can represent the positional information xand y by quantizing and by using the bit values a and b (the seconddiscrete value).

Thus, the quantizing section 112 represents the positional informationof the base station information of the base station 30 located in thebase station crowded coverage 42 by the second discrete value andcorrelates it with the base station ID and records it in the storagesection 116.

The quantizing section 112 also represents the positional information ofthe base station information of the base station 30 located in thenormal coverage 40 by the first discrete value (bit values c and d) andcorrelates it with the base station ID and records it in the storagesection 116 in the same manner. The first discrete value is convertedinto longitude and latitude based on the base point of the normalcoverage 40 and longitudinal and latitudinal quantization numbers of thenormal coverage 40. Thus, the storage section 116 has a function as astorage medium or a first storage section for storing the base stationinformation in which the quantized positional information is correlatedwith the base station IDs.

Next, precision of the first discrete value and the second discretevalue and the first quantization number and the second quantizationnumber will be explained.

Practically, 0.5 to 4 m of quantization error (positional error) of thefirst discrete value and the second discrete value may not matter inview of accuracy of the base station information input to the basestation information input section 108. Here, although the quantizationerror may be an interval between positions represented by the respectivebit values (bit values a through d) or a half of the interval of thepositions represented by the respective bit values, this will beexplained as the interval between the positions represented by therespective bit values in the following.

When each of the longitudinal distance w and the latitudinal distance hof the base station crowded coverage 42 shown in FIG. 6 is 65 km, thequantization error is 0.991 m when the base station crowded coverage 42is longitudinally and latitudinally quantized respectively by the secondquantization number of 2 bytes. The quantization error is about 0.1 mwhen, in the same manner, the normal coverage 40 is quantized by thefirst quantization number of 3 bytes which is larger than the secondquantization number.

Accordingly, the quantizing section 112 may represent the position ofthe base station 30 located in the base station crowded coverage 42 byusing any of the bit values obtained by longitudinally and latitudinallyquantizing the base station crowded coverage 42 respectively by thesecond quantization number of 2 bytes. Moreover, the quantizing section112 may represent the position of the base station 30 located in thenormal coverage 40 by using any of the bit values obtained bylongitudinally and latitudinally quantizing the normal coverage 40respectively by the first quantization number of 3 bytes. One example ofbase station information recorded in the storage section 116 by suchquantizing section 112 will be explained with reference to FIGS. 8A and8B.

FIG. 8A is an explanatory diagram showing the example of base stationinformation of the base stations 30 located in the base station crowdedcoverage 42 recorded in the storage section 116. FIG. 8B is anexplanatory diagram showing the example of base station information ofthe base stations 30 located in the normal coverage 40 recorded in thestorage section 116.

As shown in FIG. 8A, the base station information of the base stations30 located in the base station crowded coverage 42 includes the basestation IDs of 6 bytes, the bit values a of 2 bytes and the bit values bof 2 bytes. Meanwhile, as shown in FIG. 8B, the base station informationof the base stations 30 located in the normal coverage 40 includes thebase station IDs of 6 bytes, the bit values c of 3 bytes and the bitvalues d of 3 bytes.

Here, because the base stations 30 exist more densely in the basestation crowded coverage 42 than the normal coverage 40, the totalamount of the positional information contained in the base stationinformation stored in the storage section 116 is suppressed. Forinstance, there is assumed a case where a half million base stations 30are installed in the normal coverage 40, a half million base stations 30are installed in the base station crowded coverage 42, and the storagesection 116 stores the base station information of all the base stations30. In this case, the total amount of positional information containedin the base station information is 5 Mbytes from the following Equation6:

$\begin{matrix}{{{{Number}\mspace{14mu} {of}\mspace{14mu} {base}\mspace{14mu} {stations}\mspace{14mu} {located}\mspace{14mu} {in}\mspace{14mu} {normal}\mspace{14mu} {{coverage} \cdot 6}} + {{number}\mspace{14mu} {of}\mspace{14mu} {base}\mspace{14mu} {stations}\mspace{14mu} {located}\mspace{14mu} {in}\mspace{14mu} {base}\mspace{14mu} {station}\mspace{14mu} {crowded}\mspace{14mu} {{coverage} \cdot 4}}} = {{{500,{000 \cdot 6}\mspace{14mu} ({byte})} + {500,{000 \cdot 4}\mspace{14mu} ({byte})}} = {{5,000,000\mspace{14mu} ({byte})} = {5\mspace{14mu} {Mbytes}}}}} & {{{Eq}.\mspace{14mu} 6}\mspace{14mu}}\end{matrix}$

Meanwhile, when the positional information of all the base stations 30are represented by double floating-points, the total amount of thepositional information contained in the base station information is 16Mbytes from the following Equation 7:

$\begin{matrix}\begin{matrix}{{{Total}\mspace{14mu} {number}\mspace{14mu} {of}\mspace{14mu} {base}\mspace{14mu} {{stations} \cdot 16}} = {1,000,{000 \cdot 16}\mspace{14mu} ({byte})}} \\{= {16,000,000\mspace{14mu} ({byte})}} \\{= {16\mspace{14mu} {Mbytes}}}\end{matrix} & {{Eq}.\mspace{14mu} 7}\end{matrix}$

Accordingly, the total amount of the positional information contained inthe base station information may be suppressed to about 31.25% by thequantizing section 112 quantizing and representing the positionalinformation of the base stations 30 as well as implementing differentquantization depending on whether the base stations 30 are located inthe base station crowded coverage 42 or the normal coverage 40.

The base station information obtaining section 236 of the radiocommunication apparatus 20 obtains, from the information server 10, thebase station information (including information concerning the basepoint and quantization numbers) whose information amount is suppressedby the quantization described above, and records them in the storagesection 232. That is, the storage section 232 stores the base stationinformation of the base stations 30 within the normal coverage 40 whosepositional information is represented by using the bit values obtainedby quantizing the positions by setting the normal coverage 40 as thequantization coverage and the first quantization number as thequantization number as shown in FIG. 8B. The storage section 232 alsostores the base station information of the base stations 30 within thebase station crowded coverage 42 whose positional information isrepresented by using the bit values obtained by quantizing the positionsby setting the base station crowded coverage 42 as the quantizationcoverage and the second quantization number that is smaller than thefirst quantization number as the quantization number as shown in FIG.8A.

The position estimating section 224 can extract, from the storagesection 232, the positional information of the base station 30 that isthe source of the signals received by the communication section 216represented by the bit values, and can find the longitude and latitudeof the base station 30 according to Equations 4 and 5 to use them forestimating the position. For instance, when the position estimatingsection 224 judges that the base station 30 is located in the basestation crowded coverage 42 based on the bit numbers of the positionalinformation of the base station 30 that is the source of the signalsreceived by the communication section 216, it can find the longitude andlatitude of the base station 30 by applying Equations 4 and 5. Incontrast, when the position estimating section 224 judges that the basestation 30 is located in the normal coverage 40, it can find thelongitude and latitude of the base station 30 by applying Equationscorresponding to Equations 4 and 5.

In addition, because the perimeter of the earth at the equator is 40,000km, a quantization error is 2.384 m when the longitude is quantized by 3bytes (a quantization number of third power of 256), i.e.,40,000,000/256̂3=2.384. In the same manner, a quantization error islatitudinally 1.19 m from 20,000,000/256̂3=1.19.

Accordingly, the quantizing section 112 of the information server 10 maysimply represent an arbitrary position on the earth by using discretevalue obtained by quantizing latitudinally and longitudinallyrespectively by 3 bytes. According to this method, when a half millionbase stations 30 are installed in the normal coverage 40 and a halfmillion base stations 30 are installed in the base station crowdedcoverage 42 similarly to the case described above, the total amount ofpositional information contained in the base station information is 6Mbytes from the following Equation 8. Therefore, it is effective tosimply represent an arbitrary position on the earth by using thediscrete value obtained by quantizing latitudinally and longitudinallyrespectively by 3 bytes from an aspect of reducing the informationamount of the base station information.

$\begin{matrix}\begin{matrix}{{{Total}\mspace{14mu} {number}\mspace{14mu} {of}\mspace{14mu} {base}\mspace{14mu} {{stations} \cdot 6}} = {1,000,{000 \cdot 6}\mspace{14mu} ({byte})}} \\{= {6,000,000\mspace{14mu} ({byte})}} \\{= {6\mspace{14mu} {Mbytes}}}\end{matrix} & {{Eq}.\mspace{14mu} 8}\end{matrix}$

The position estimating section 224 of the radio communication apparatus20 can estimate the position more accurately when it receives signalsfrom more base stations 30. Accordingly, the quantization error in thebase station crowded coverage 42 may be larger than that in the normalcoverage 40 in order to realize the estimation of position in the basestation crowded coverage 42 and the estimation of position in the normalcoverage 40 made by the position estimating section 224 at the samedegree of precision.

Then, the quantizing section 112 of the information server 10 mayquantize so that the quantization error in the base station crowdedcoverage 42 becomes larger than the quantization error in the normalcoverage 40. Such configuration allows bit numbers representing positionof the base station located in the base station crowded coverage 42 tobe suppressed while keeping the precision of the estimation of positionperformed by the position estimating section 224.

[2-3] Operations of Radio Communication Apparatus and Information Server

The configurations of the radio communication apparatus 20 and theinformation server 10 have been explained above with reference to FIGS.2 through 8. Next, the position estimating method executed in the radiocommunication apparatus 20 and the information server 10 will beexplained with reference to FIG. 9.

FIG. 9 is a sequence diagram showing a flow of the position estimatingmethod executed in the radio communication apparatus 20 and theinformation server 10. First, base station information is input to thebase station information input section 108 of the information server 10(S304). Then, the quantizing section 112 judges whether positionindicated by positional information contained in the base stationinformation is contained in the base station crowded coverage 42 or thenormal coverage 40 and quantizes the positional information by a methodcorresponding to a result of the judgment (S308).

Then, the quantizing section 112 records the base station informationcontaining the quantized positional information in the storage section116 (S312). Subsequently, when the base station information obtainingsection 236 of the radio communication apparatus 20 requests the basestation information to the information server 10 (S316), the informationserver 10 transmits the base station information recorded in the storagesection 116 to the radio communication apparatus 20 (S320).

In addition, the transmission of the base station information from theinformation server 10 to the radio communication apparatus 20 may beperiodically carried out. Moreover, when the radio communicationapparatus 20 has the base station information already stored, theinformation server 10 may transmit only an updated portion of the basestation information to the radio communication apparatus 20.

On obtaining the base station information from the information server10, the base station information obtaining section 236 records theobtained base station information in the storage section 232 (S324).When the communication section 216 receives signals from surroundingbase stations 30 after that (S328), the position estimating section 224estimates the position of the radio communication apparatus 20 based onthe received signals and the base station information stored in thestorage section 232 (S332).

For instance, the position estimating section 224 extracts positionalinformation correlated with the base station ID contained in eachreceived signals from among positional information quantized andcontained in the base station information stored in the storage section232. Then, the position estimating section 224 can decode the extractedand quantized positional information into latitude and longitude andestimate the position of the radio communication apparatus 20 byperforming the arithmetic operation shown in Equation 1 by using thedecoded latitude and longitude.

After that, the application section 228 can perform processes ofinforming the user of the position estimated by the position estimatingsection 224, requesting the user for authentication processingcorresponding to the position estimated by the position estimatingsection 224, and the like.

[3] CONCLUSION

As described above, the storage section 232 of the radio communicationapparatus 20 according to the present embodiment stores the base stationinformation of the base stations 30 within the normal coverage 40 whosepositional information is represented by bit values (first discretevalue) obtained by quantizing the positions by setting the normalcoverage 40 as the quantization coverage and the first quantizationnumber as the quantization number. The storage section 232 also storesthe base station information of the base stations 30 within the basestation crowded coverage 42 whose positional information is representedby using bit values (second discrete value) obtained by quantizing thepositions by setting the base station crowded coverage 42 as thequantization coverage and the second quantization number that is smallerthan the first quantization number as the quantization number.

Because the second quantization number is smaller than the firstquantization number in the configuration described above, an informationamount required for representing the second discrete value may besuppressed more than an information amount required for representing thefirst discrete value. Here, the density of the base stations located inthe base station crowded coverage 42 is higher than the density of thebase stations located in the normal coverage 40. Accordingly, the radiocommunication apparatus 20 can keep the positional information of thebase stations 30 located in the normal coverage 40 and in the basestation crowded coverage 42 while suppressing their information amountas compared to a case of simply quantizing the normal coverage 40 andthe base station crowded coverage 42 altogether.

In addition, although a preferred embodiment of the present inventionhas been described with reference to the accompanying drawings, thepresent invention is not limited thereto as a matter of course. It isobvious to those skilled in the art that various alternations andmodifications may be made without departing from the scope of the claimsand thus are intended for inclusion within the technical scope of thepresent invention.

For example, although the case of distinctively storing only the basestation information contained in one normal coverage 40 and the basestation information contained in one base station crowded coverage 42has been explained in the embodiment described above, the presentinvention is not limited to such example. A modified example will beexplained below with reference to FIG. 10.

FIG. 10 is an explanatory diagram showing the exemplary modification ofthe normal coverage 40 and the base station crowded coverage 42. Asshown in FIG. 10, a plurality of base station crowded coverages 42 suchas a base station crowded coverage 42A and a base station crowdedcoverage 42B may be contained in one normal coverage. Moreover, the basestation crowded coverage 42 is not limited to be rectangular and mayhave an arbitrary shape such as an elliptical shape as shown in a basestation crowded coverage 42C or a triangular shape. Moreover, arelationship of quantization numbers applied to the base station crowdedcoverage 42A, 42B and 42C is not specifically limited.

Furthermore, there may be a base station crowded coverage 42 like a basestation crowded coverage 42D that is set within the base station crowdedcoverage 42A. In this case, quantization numbers applied to the basestation crowded coverage 42D are smaller than quantization numbersapplied to the base station crowded coverage 42A, and from a point ofview of the base station crowded coverage 42D, the base station crowdedcoverage 42A may correspond to the normal coverage 40.

Moreover, although the case where the quantizing section 112 quantizesthe positional information into bit values corresponding to thelongitudinal and latitudinal directions has been explained above, thepresent invention is not limited to such case. For instance, thequantizing section 112 may quantize the positional information into abit value in which a solution of an divided integer corresponds to thelongitudinal direction and into a bit value in which the remaindercorresponds to the latitudinal direction. The quantizing section 112 mayalso quantize the positional information on a polar coordinate plane.Furthermore, the quantization method for the normal coverage 40 may bedifferent from the quantization method for the base station crowdedcoverage 42.

The quantizing section 112 may also quantize the positional informationinto bit values corresponding to a size of a center angle of asinusoidal wave having arbitrary amplitude and frequency.

The respective steps in the process of the radio communication apparatus20 and the information server 10 of the present specification are notalways necessary to be processed in chronological order in accordancewith the order described in the sequence diagram and may includeprocesses executed in parallel or individually (e.g., a parallelprocessing or process by objects).

It is also possible to create a computer program for making the hardwaresuch as the CPU 201, the ROM 202 and the RAM 203 built in the radiocommunication apparatus 20 and the information server 10 exhibitequivalent functions with the respective configurations of the radiocommunication apparatus 20 and the information server 10 describedabove. Moreover, there may be provided a storage medium storing thecomputer program. It is also possible to configure the respectivefunctional blocks shown in the functional block diagram of FIG. 3 byhardware, thereby realizing the series of processes by hardware.

1. A position estimating system comprising: a radio communicationapparatus capable of wirelessly communicating with one or more basestations; and an information server capable of communicating with theradio communication apparatus, wherein the information server includes aquantizing section for representing positional information of a firstbase station located in a first coverage by using a first discrete valueobtained by quantizing the position of the first base station by settingthe first coverage as a quantization coverage and a first quantizationnumber as a quantization number and for representing positionalinformation of a second base station located in a second coverage whosearea is narrower than the first coverage and where the base stations aremore densely installed than the first coverage by using a seconddiscrete value obtained by quantizing the position of the second basestation by setting the second coverage as a quantization coverage and asecond quantization number that is smaller than the first quantizationnumber as a quantization number, a first storage section for storingbase station information in which the positional information representedby using the first discrete value or the second discrete value by thequantizing section is correlated with identification information of thebase station, and a transmitting section for transmitting the basestation information to the radio communication apparatus, and whereinthe radio communication apparatus includes an obtaining section forobtaining the base station information that is transmitted from thetransmitted section and stored in the first storage section, a secondstorage section for storing the base station information obtained by theobtaining section, a receiving section for receiving radio signalscontaining the identification information of the base stationtransmitted from the base station, and a position estimating section forextracting the positional information of the base station indicated bythe identification information contained in the radio signals from thepositional information stored in the storage section and estimating theposition of the radio communication apparatus based on the extractedpositional information.
 2. A radio communication apparatus capable ofwirelessly communicating with one or more base stations, comprising: astorage section for correlating and storing positional information andidentification information of the base station; a receiving section forreceiving radio signals transmitted from the base station and containingthe identification information of the base station; and a positionestimating section for extracting the positional information of the basestation indicated by the identification information contained in theradio signals from the positional information stored in the storagesection and estimating the position of the radio communication apparatusbased on the extracted positional information, wherein in the storagesection, the positional information of a first base station located in afirst coverage is represented by using a first discrete value obtainedby quantizing the position of the first base station by setting thefirst coverage as a quantization coverage and a first quantizationnumber as a quantization number and the positional information of asecond base station located in a second coverage whose area is narrowerthan the first coverage and where the base stations are more denselyinstalled than the first coverage is represented by using a seconddiscrete value obtained by quantizing the position of the second basestation by setting the second coverage as a quantization coverage and asecond quantization number that is smaller than the first quantizationnumber as a quantization number.
 3. The radio communication apparatusaccording to claim 2, wherein the first quantization number or thesecond quantization number is a value that keeps a quantization error ofthe first discrete value or the second discrete value within a range of0.5 m to 4 m.
 4. The radio communication apparatus according to claim 3,wherein the first coverage is a coverage excluding the second coveragefrom a predetermined coverage overlapping with the second coverage. 5.The radio communication apparatus according to claim 4, wherein aplurality of second coverages are contained in the predeterminedcoverage.
 6. The radio communication apparatus according to claim 1,wherein the quantization error of the second discrete value is largerthan the quantization error of the first discrete value.
 7. A programfor operating a computer as a radio communication apparatus capable ofwirelessly communicating with one or more base stations, comprising: areceiving section for receiving radio signals transmitted from the basestation and containing identification information for identifying thebase station; and a position estimating section for extracting thepositional information of the base station indicated by theidentification information contained in the radio signals from a storagemedium correlating and storing the positional information indicating theposition of the base station and the identification information, andestimating the position of the radio communication apparatus based onthe extracted positional information, wherein in the storage medium, thepositional information of a first base station located in a firstcoverage is represented by using a first discrete value obtained byquantizing the position of the first base station by setting the firstcoverage as a quantization coverage and a first quantization number as aquantization number, and the positional information of a second basestation located in a second coverage whose area is narrower than thefirst coverage and where the base stations are more densely installedthan the first coverage is represented by using a second discrete valueobtained by quantizing the position of the second base station bysetting the second coverage as a quantization coverage and a secondquantization number that is smaller than the first quantization numberas a quantization number.
 8. A position estimating method executed in aradio communication apparatus capable of wirelessly communicating withone or more base stations, comprising the steps of: receiving radiosignals transmitted from the base station and containing identificationinformation for identifying the base station; and extracting thepositional information of the base station indicated by theidentification information contained in the radio signals from a storagemedium correlating and storing the positional information indicating theexisting position of the base station and the identificationinformation, and estimating the position of the radio communicationapparatus based on the extracted positional information, wherein in thestorage medium, the positional information of a first base stationlocated in a first coverage is represented by using a first discretevalue obtained by quantizing the position of the first base station bysetting the first coverage as a quantization coverage and a firstquantization number as a quantization number, and the positionalinformation of a second base station located in a second coverage whosearea is narrower than the first coverage and where the base stations aremore densely installed than the first coverage is represented by using asecond discrete value obtained by quantizing the position of the secondbase station by setting the second coverage as a quantization coverageand a second quantization number that is smaller than the firstquantization number as a quantization number.
 9. An information servercapable of communicating with a radio communication apparatus capable ofwirelessly communicating with one or more base stations, comprising: aquantizing section for representing positional information of a firstbase station located in a first coverage by using a first discrete valueobtained by quantizing the position of the first base station by settingthe first coverage as a quantization coverage and a first quantizationnumber as a quantization number, and for representing positionalinformation of a second base station located in a second coverage whosearea is narrower than the first coverage and where the base stations aremore densely installed than the first coverage by using a seconddiscrete value obtained by quantizing the position of the second basestation by setting the second coverage as a quantization coverage and asecond quantization number that is smaller than the first quantizationnumber as a quantization number; a storage section for storing basestation information in which the positional information represented byusing the first discrete value or the second discrete value by thequantization section are correlated; and a communication section fortransmitting the base station information stored in the storage sectionto the radio communication apparatus.